Monday, May 14, 2012
Future HDDs To Have A Data Areal Density Of 5Tbit /sqi

The latest developments in magnetism and associated
technologies were presented at the International
Magnetics Conference, INTERMAG 2012, held in in
Vancouver from May 7th to May 11th, 2012.

Many presentations were related to candidate
technologies that could be applied to hard disk drives
and increase their areal data density - the number of
bits that can be recorded per unit area.

Today's hard drive resembles a small record player
that's capable of stacking its disks, or platters, to
hold up to eight of them at a time. Each platter is
covered with a magnetic film that is ingrained with tiny
particles called bits. When a read-write head passes
over the bits, it either magnetically aligns the
particles to record information (turning them into
series of 1's and 0's), or it reads them in order to
access previously-stored data. These operations take
place at phenomenal speeds; the platters spin around
thousands of times per minute, and both sides of them
are scanned simultaneously by read-write heads.

A challenge for increasing the areal density is the
superparamagnetic effect. As hard drives become capable
of storing more information and accessing it at faster
speeds, their data becomes more susceptible to
corruption.

Currently the HDD industry has improved existing HDD
technologies but the data density limit of 1Tbit /
square inch is very close. Ongoing research and
development has leaded to new techniques that could
break this limit. The main approaches are the following:

Bit Patterned media is a potential magnetic storage
technology to record data in a uniform array of magnetic
cells, storing one bit per cell, as opposed to regular
hard-drive technology, where each bit is stored across a
few hundred magnetic grains. It uses nanolithography to
pattern the underlying media with the magnetic cells
allowing for greater areal density than would normally
be possible.

At Intermag 2012, Toshiba showcased a FePt bit-patterned
media fabricated by a self-assembled polymer mask. The
disc was 3.2nm thick and used a FePt alloy. The
prototype media boasts an areal density of 5Tb per
square inch.

Heat-assisted magnetic recording (HAMR) is a technology
that magnetically records data on high-stability media
using laser thermal assistance to first heat the
material. HAMR takes advantage of high-stability
magnetic compounds such as iron platinum alloy. These
materials can store single bits in a much smaller area
without being limited by the same superparamagnetic
effect that limits the current technology used in hard
disk storage. The only catch being that they must be
heated to apply the changes in magnetic orientation.
HAMR was developed by Fujitsu in 2006.

HAMR's challenges include solving a range of engineering
challenges such as how to integrate laser diodes and
recording heads. Patterned media proponents have yet to
demonstrate ways to cover a full disk with tiny magnetic
dots in a way that can be mass produced.

At Intermag 2012, a joint research team from University
of Rochester and Western Digital proposed the use of a
Fresnel lens (Paper: "An On-Wafer Diffractive Lens for
Energy Assisted Magnetic Recording Technology") as
focusing elements for the laser light. Fresnel lenses
can be easily manufactured and can be applied using
a lithography technique, decreasing the implications up
and down the hard disk supply chain.

Using MAMR, a drive head emits a microwave field that
excites the electrons in the media building up energy
that eases the process of writing data. The process uses
a localized high frequency ac magnetic field generated
by a magnetic thin film stack integrated with existing
recording heads.

A joint research group at Keio University and TDK
showcased a on microwave-assisted writing of 500
Gb/sqi-class perpendicular medium. Hitachi, Ltd.'s
simulation using microwave assistance also showed that
the magnetic recording was possible at avery high
density of 6.3Tbit/sqi.

Single magnetic recording technology (SMR) is actually
an extension to today's perpendicular recording
technology. The technique uses overlapping tracks and
deliver drives with 1.5 to 2 Terabits of data per square
inch of a disk.

Of course, the road to commercialization of most of
these technologies is still a long.